The present invention relates to a method of forming structures on a semiconductor wafer by lithographic and subsequent ion implant steps. In particular the lithographic steps are photo-lithographic steps.
The general method of doping a semiconductor is based on preparing a mask by lithographic steps and subsequently implanting ions in the semiconductor so as to determine its conductivity which depends on the doping profile and the doping level in specific areas.
If different areas with different doping characteristics are desired in a semiconductor the same implantation procedure must be carried out repeatedly, each time with a new reticle so as to expose, develop and etch another area on the semiconductor for the subsequent implantation procedure. This is time consuming and costly.
It is therefore desirable to have a method of forming several implant resist layers with which the preparation of the resist for all doping profiles is feasible in a single processing step.